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cmd/lopower: refactor in prep for DNS filtering

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Change-Id: I4a4c2d8331fbc2a7aaab4e75c27b29afaaeb0300
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick 2024-11-03 12:08:37 -08:00 committed by Anton Tolchanov
parent ddc5d14d09
commit 4c516c2249
1 changed files with 24 additions and 6 deletions
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30
cmd/lopower/lopower.go
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@ -640,6 +640,28 @@ func (lp *lpServer) startTSNet(ctx context.Context) {
}
}
// filteredDNSQuery wraps the MagicDNS server response but filters out A record responses
// for *.ts.net if IPv4 is not enabled. This is so the e.g. a phone on a CGNAT-using
// network doesn't prefer the "A" record over AAAA when dialing and dial into the
// the carrier's CGNAT range into of the AAAA record into the Tailscale IPv6 ULA range.
func (lp *lpServer) filteredDNSQuery(ctx context.Context, q []byte, family string, from netip.AddrPort) ([]byte, error) {
m, ok := lp.tsnet.Sys().DNSManager.GetOK()
if !ok {
return nil, errors.New("DNSManager not ready")
}
res, err := m.Query(ctx, q, family, from)
if err != nil {
return nil, err
}
if *includeV4 {
return res, nil
}
// TODO(bradfitz): filter out *.ts.net A records.
return res, nil
}
// caller owns the raw memory.
func (lp *lpServer) handleDNSUDPQuery(raw []byte) {
var pkt packet.Parsed
@ -647,12 +669,8 @@ func (lp *lpServer) handleDNSUDPQuery(raw []byte) {
if pkt.IPProto != ipproto.UDP || pkt.Dst.Port() != 53 || !lp.c.IsLocalIP(pkt.Dst.Addr()) {
panic("caller error")
}
m, ok := lp.tsnet.Sys().DNSManager.GetOK()
if !ok {
log.Printf("DNSManager.Get: not ready")
return
}
dnsRes, err := m.Query(context.Background(), pkt.Payload(), "udp", pkt.Src)
dnsRes, err := lp.filteredDNSQuery(context.Background(), pkt.Payload(), "udp", pkt.Src)
if err != nil {
log.Printf("DNS query error: %v", err)
return